Ecosystems: Coral Reefs

Flower Garden Banks National Marine Sanctuary

This photograph depicts the landscape of the East and West Flower Garden Banks. It illustrates the high coral coverage (around 50 percent) and competition for space between colonies. (Photo: Frank and Joyce Burck)

Reef Structure and Physical Features: The Flower Garden Banks are small underwater mountains near the edge of the Outer Continental Shelf in the northwestern Gulf of Mexico. These banks, known as salt domes, are the result of uplifting caused by pockets of salt beneath the sea floor.

Atop the salt domes sit some of the healthiest coral reefs in the Caribbean and Gulf of Mexico. Deeper areas of the salt domes are home to extensive mesophotic reefs.

The nearest tropical reefs to the Flower Garden Banks are 400 miles away off the coast of Tampico, Mexico. Scientists believe that corals at the Flower Gardens probably originated from Mexican reefs when currents in the western Gulf of Mexico carried the young corals northward. A few of these larvae were lucky enough to settle on the hard substrate (sea floor) of the Flower Garden Banks salt domes.

Amazingly, this location in the northwestern Gulf of Mexico provided all the comforts of home for hard corals: a hard surface for attachment, warm water temperatures (between 68 and 84 degrees Fahrenheit), a steady food supply, and clear sunlit water. Visibility around these reefs is usually about 100 ft (30 m) or better and light penetrates well to 280 ft (85 m).

Coral Species and Cover: Coral cover on the reef cap (0-130 ft, 0-40 m) at the Flower Garden Banks is over 50%. This is the highest coral cover of any site in the Caribbean and Gulf of Mexico. Of the 23 species of coral present, the predominant are large boulder-shaped colonies of star coral (Orbicella and Montastraea species) and brain coral (Pseudodiploria and Colpophyllia species), with a few areas of the sanctuary dominated by smaller branching coral (Madracis species). The coral reefs of Flower Garden Banks National Marine Sanctuary also produce one of the most visually prolific mass coral spawning events in the entire Caribbean.

Noticeably absent are shallow water octocorals, such as sea fans and sea whips. However, exploration of deeper mesophotic reef areas within the sanctuary shows a large number of octocorals and black corals (Antipatharia species).

Other Fauna and Flora: The Flower Garden Banks are home to about 150 species of algae, over 1,000 macro-invertebrate species, and more than 300 fish species. Loggerhead and Hawksbill Sea Turtles, Manta Rays, Spotted Eagle Rays, Whale Sharks, and schooling Scalloped Hammerhead Sharks are some of the larger, more noticeable wildlife that occur in the sanctuary.